This invention relates to electric motors or to other electric dynamo machines, and more particularly relates to a centrifugal actuator for actuating a motor starting switch which in turn controls energization of the starting winding in the motor in response to the speed of rotation of the motor.
In many conventional electric motors, such as in single phase induction motors, a rotating magnetic field is produced by the use of a main winding and a starting winding. These windings are so designed and arranged within the motor that during startup of the motor, sufficient starting torque is attained. Once the motor reaches a predetermined operational speed, a switch responsive to the rotational speed of the motor is opened so as to deenergize the starting winding. Upon the motor speed slowing below another predetermined speed of operation (e.g., upon shut down of the motor), the switch is closed so that it will energize the starting winding of the motor upon restarting the motor. The switch is operated by a centrifugal actuator.
Heretofore, centrifugal actuators were typically mounted on the rotor shaft of the motor and were rotatable therewith. The motor starting switch was oftentimes secured to the frame or to the end shield of the motor and a movable actuator finger or linkage operatively coupled the motor starting switch to the centrifugal actuator, the latter being fixed on the rotor shaft. Thus, the relative position of the motor starting switch and the centrifugal actuator on the shaft had to be such that the motor starting switch would be actuated upon movement of the centrifugal actuator in response to the motor rotating at its predetermined operational speed.
During manufacture of motors, the rotor shaft is shimmed with end play washers so as to insure that the rotor is properly positioned with respect to the stator in the motor housing. Once the rotor with the centrifugal actuator thereon is fixed or shimmed relative to the motor housing or end shield, the motor starting switch and its actuator finger or linkage is positioned with respect to the centrifugal actuator so as to insure that the motor starting switch will be actuated by the centrifugal actuator at the above-mentioned predetermined operating speed of the motor. As will be appreciated, shimming of the rotor shaft and the accurate positioning and adjustment of the motor starting switch are time consuming and therefore relatively expensive operations in the manufacture of electric motors. Furthermore, electric motors oftentimes develop end play of the rotor shaft relative to the end shields of the motor during use of the motor. With prior centrifugal actuators, if this rotor shaft end play would exceed certain limits, the motor starting switch would not be operated by the centrifugal actuator. Thus, the motor starting switch could fail to deenergize the starting windings which in turn could lead to failure of the starting winding, or the motor starting switch could fail to energize the starting windings and the motor would fail to start.
Reference may be made to U.S. Pat. Nos. 3,271,602, 3,609,421, 3,872,691 and 4,034,173 for certain prior art electric motors with centrifugal starting switches in the same broad category as this invention.